This seems like a sensible enough reaction. The primary debates are not watched by all that many people, but the big moments are replayed for days afterward by the news networks and on the Web. This was a big moment; the presidential scholar Larry Sabato wrote that it was “the most devastating moment of any modern primary debate.” It will reinforce some core negative perceptions about Mr. Perry: that he is a bad debater, that he is a lightweight, and that he is someone who is not quite ready for prime time. Had another candidate made the same mistake, that candidate might have gotten a mulligan. But Mr. Perry used his mulligans up long ago after stammering answers and poor overall performances in several of his previous debates.

At the same time, it should be remembered how volatile the Republican primary process has been. This week’s comeback kid — Newt Gingrich — once had a campaign so moribund that many assumed it would end at some point during the summer. Herman Cain’s numbers had slumped in the summer, before he suddenly rocketed toward the front of the pack five or six weeks ago. I know it looks bad for Mr. Perry — but he still has some things working in his favor, like money, a good team of advisers and his impressive jobs credentials down in Texas. Assuming that the gaffe causes some further slippage in his polling, might there be time for him to come back as well?

Here is the problem for Mr. Perry: there is not all that much time left. Iowa will vote less than two months from today, with New Hampshire and South Carolina following on its heels. This is about the point in time at which voters, donors and party officials need to think tactically, betting on a horse they think can win. Thus, Mr. Perry’s demise could be a self-fulfilling prophecy: If everyone thinks he is going to lose, he almost certainly will.

My guess is that some Republicans will be inclined to step in, look at the struggles of Mr. Perry and Mr. Cain, and declare Mitt Romney the winner by a technical knockout. That may or may not go over well with voters, but Mr. Romney could begin to consolidate his support in the party establishment.

Meanwhile, those voters who are not inclined toward Mr. Romney might see a credible-enough alternative in Mr. Gingrich, who performed well at the Wednesday night debate. Mr. Gingrich’s campaign has all sorts of problems — some of which will be exposed if he rises further in the polls. But voters may conclude, perhaps not wrongly, that he is nevertheless more viable than Mr. Perry at this stage.

Perhaps the worst news of all for Mr. Perry, although it is a little anecdotal at this stage, is that some of his major donors do not seem inclined to stand behind him. That could send his campaign into a death spiral, as other donors, supporters and staff members jump ship. Mr. Perry does have a decent amount of cash on hand, but a fully staffed campaign burns money quickly, especially once the actual voting nears.

If I were Mr. Perry, I would make an “all-in” bet on Iowa. Forget about the other states: you may not have the resources to compete in them anyway. Iowa Republicans have been friendly to Texans in the past, and the state can play to his strengths as a retail campaigner. More importantly, winning Iowa can provide tangible evidence that your campaign is viable, something that even Mr. Perry’s supporters must be questioning now.

Still, this is normally the strategy that a second- or third-tier candidate pursues — and not a front-runner. If you think of Mr. Perry as a second-tier candidate, the 25-to-1 odds you can now get on him at Intrade seem roughly fair. But I am not sure they are a lot higher than that. It is one thing to regain forward momentum when your campaign seems stalled, but another when it looks to be headed downhill.

Nate Silver is the founder and editor in chief of FiveThirtyEight. @natesilver538